German Auslegeschrift No. DE-AS 23,39,170 discloses such a window shade, in which a winding shaft, which is rotatably mounted at its ends on stationary pivot pins, can be coupled at least at one of its ends with a drive member and has at least one rolling body, which acts as a locking member and interlocks the winding shaft loaded in the roll-off direction of the shade with the pivot pin.
In another prior-art device according to U.S. Pat. No. 4,372,432, the pivot pin at both ends of the winding shaft can be nonrotatably fastened to a wall, ceiling or the like with a bracket, wherein the bracket engages a slot arranged on the outer front surface of the pivot pin.
Such a shade can be locked in various positions. The locking member consists of a coil spring, which acts in the manner of a sliding clutch and fixes the shade by frictional connection with a sleeve.
In addition, a great variety of so-called spring-type window shades have been known, which have locking members consisting of catches, which are arranged radially movably in relation to the window shade axis and cooperate with stationary abutments on the winding shaft. Free movement is achieved due to the radially movable linkage of the catches during rapid rotation of the window shade shaft, so that the catches come into contact with the abutments under their own weight only during slow rotation of the window shade shaft and bring about blocking between the window shade shaft and the stationary pin.